The control and regulation of the pressure applied by a press to a work piece is commonly achieved by monitoring the output pressure exerted by the hydraulic or pneumatic pump which supplies the press mechanism. This monitoring is accomplished via manometers and other types of pressure gauges and transducers. The pressure thus measured fails to take into account the friction and drag forces inherent to the press mechanism. The measurements cannot be accurately corrected if these parasitic forces are either unknown or tend to vary over the total range of the press.
If the press is to be used over a wide range of pressures, the monitoring gauge or transducer must be able to withstand the maximum pressure. The resolution or sensitivity of the gauge, which normally is a fraction of its fullest-scale measurement capability, can seriously affect the accuracy of any measurement in the lowest portion of the range. The problem can only be palliated by successively substituting various gauges or transducers for different ranges and sensitivities in commensuration with the maximum pressure to be applied to the work piece. This substitution can be rather cumbersome or totally impractical in many applications.
In laboratory presses ued for testing the strength of certain material and in certain manufacturing presses used in the molding of delicate parts, it is often desirable to obtain a precise and instantaneous measurement of the actual force applied to the work piece in order to achieve a more perfect control and regulation of that force. It is also desirable that this type of press be controllable with a high degree of accuracy over a wide range of pressures by means of automated process controllers free of any mechanical switching step and other slow and erratic procedures.